1. Field of the Invention
The present invention relates to a backlash preventing structure for a steering column which is equipped in an automobile.
2. Description of the Related Art
A steering column, which is a device for changing the direction in which an automobile runs, may permit a driver to adjust a steering wheel by tilting the steering wheel in the vertical direction and moving up or down the steering wheel along a steering shaft in order for the driver to ensure an optimal driving posture for his physical constitution.
However, in such a steering column, backlash in a telescopically movable structure would not only give unpleasant feeling to a driver who manipulates a steering wheel, but also cause a degradation in a steering wheel supporting rigidity, so that vibrations of the engine, vibrations of the chassis, when running on an irregular ground, and the like would cause the steering wheel to vibrate, thus spoiling manipulation feeling of the driver, and reducing the commercial value of the automobile itself.
The applicant has therefore proposed a structure for preventing the foregoing backlash (see Laid-open Japanese Utility-Model Registration Application No. 6-74562). The backlash preventing structure is shown in FIGS. 8 and 9.
FIG. 8 is a lateral sectional view of the conventional backlash preventing structure, and FIG. 9 is a cross-sectional view taken along a line C-C in FIG. 8. In these figures, a cylindrical upper jacket 101 is fixed on a chassis, and a cylindrical movable sleeve 102 is slidably fitted on the upper jacket 101. A steering shaft, not shown, is coupled to the movable sleeve 102, and a steering wheel, not shown, is securely connected to one end of the steering shaft.
A square window hole 102a is formed through the top of the movable sleeve 102, and a rectangular plate 103 is fitted into the window hole 102a. The plate 103 has an inner surface formed in an arcuate shape which is in contact with the outer peripheral surface of the upper jacket 101. A protrusion 103a is formed at the center of the inner surface of the plate 103. Then, the protrusion 103a is fitted into an elongated hole 101a of the upper jacket 101, which is formed long in a direction in which it slides, thereby preventing the movable sleeve 102 from rotating and limiting the stroke of the movable sleeve 102.
On the top of the plate 103, a pair of press members 104 are spaced apart from each other, and are urged in directions opposite to each other by a spring 105 interposed between the press members 104. These press members 104 and spring 105 are housed in a cover 106 which is attached to a pair of seats 102b integrally implanted on the edge of the window hole 102a of the movable sleeve 102 with screws 107.
Here, the top of each press member 104 is formed into a tapered surface 104a which is in contact with a tapered region 106a of the cover 106.
Thus, the foregoing plate 103, press members 104, spring 105, cover 106, and screws 107 make up the backlash preventing structure. According to this backlash preventing structure, since the two press members 104 are urged in the directions opposite to each other by the spring 105, the press members 104 act to press the plate 103 onto the upper jacket 101 through a wedging action made by the tapered surface 104a in contact with the tapered region of the cover 106, thus preventing backlash of the movable sleeve 102 with respect to the upper jacket 101.
However, since the foregoing backlash preventing structure requires a total of seven parts, i.e., one plate 103, two press members 107, one spring 105, one cover 106, and two screws 107, these parts cause an increase in cost. Also, since the assembly of the backlash preventing structure involves mounting the two pressing members 104 with the spring 105 kept in a compressed state, dedicated assembling tools must be provided, thus implying a problem with respect to the ease of the assembly of the backlash preventing structure.
Also, the fixation of the plate 103 in the axial direction depends on a frictional force resulting from the urging force of the spring 105, and in principle, the plate 103 is permitted to move in the axial direction, so that during a telescopic operation (a sliding operation of the movable sleeve 102 along the steering shaft), the plate 103 can move in the axial direction to generate hammering noise with the movable sleeve 102.